Development of pantograph-type robot arm equipped with 3-dimentional gravity compensation mechanism

In this paper, we described the principle, design prototype and evaluation of of 3-dimensional gravity compensation mechanism for human coexistence robot. In this mechanism, it is possible to realize 3-dimensional gravity compensation by rotating the entire pantograph mechanism at the root and arranging actuators as counterweights so as to balance moments of all joints. We derive the relationship such as the link length and the center of gravity position to realize this. In addition, by constructing a mechanism that adds compensation force using wires, the entire arm is made as compact as possible. From the joint torque simulation and experiment of the prototype arm, it was confirmed that the arm can be driven with joint torque of 15% to 25% with respect to the arm without compensation meshanism. In addition, it was found that the effect of reducing the torque supporting the arm's own weight was larger than the influence of the increase of the moment of inertia by counterweight.